The interaction of actin with the cytoplasmic surface of the human erythrocyte membrane is being investigated to determine if lipids or proteins form the site of interaction since we have found significant binding of actin to purified lipids. If, as originally suspected, proteins form the site of actin binding, we plan to use monospecific antibodies to determine which protein(s) forms that site. The structure of the actin-membrane complex is being studied by electron microscopy. Also, we are investigating the molecular basis for Concanavalin A effects on erythrocyte shape changes. The binding of Con A to erythrocyte receptors affects the ATP-dependent shape change of erythrocyte ghosts as well as drug-induced shape changes in whole cells. In order to test several mechanisms for this effect, we are following protein phosphorylation and oxidation as well as the effect of specific antibodies on this process. BIBLIOGRAPHIC REFERENCES: Sheetz, M.P., Painter, R.G., and Singer, S.M. (1976) Compensatory Shape Changes Induced in Membranes. J. Cell Biol. Sheetz, M.P. and Singer, S.J. (1976) Equilibrium and Kinetic Effects of Drugs on Shapes of Human Erythrocytes. J. Cell Biol.